In the field of roofing, increasing use is being made of membrane roofing materials such as EPDM (ethylene propylene diene monomer) and neoprene. Sheets of such materials are generally prepared by a double calendering process in which two sheets of uncured material are pressed together by rollers to form a single sheet. The composite single sheet is then generally coated with talc, wound into a roll and cured.
Although this calendering process virtually eliminates leakage problems arising from small defects such as pinholes in either of the two original sheets, it increases the cost of the finished product.
The membrane roofing materials are available in sheets of standard widths. Successive sheets of the membrane roofing material are spliced together to form a continuous sheet which covers the roof. Lap joints are typically used to splice adjacent sheets of roofing material. To form such a joint, sheets of the material are positioned adjacent to one another such that they overlap about three inches along the edges to be joined. The edge of the overlying sheet is then folded back such that the contact surfaces of the the edges are exposed. The overlapping surfaces are then cleaned with a solvent such as hexane, toluene or white gasoline to remove talc or other foreign material which might impair the strength of the bond. A contact adhesive is then applied to the contact surfaces and allowed to dry. The sheets are then repositioned in overlapping relation and the overlapping areas are pressed together by a roller which is rolled along the joint.
The strength of the lap joint may be improved by use of a primer. Such primer is best applied to the overlapping surfaces of the membrane roofing material after cleaning with solvent but before application of the contact adhesive. The primer may also be used by scrubbing or brushing it onto the overlapping surfaces without cleaning.
This method of joining sheets of roofing material is extremely slow and labor intensive. In addition, the lap joint formed by this method must be sealed with a caulking compound to prevent penetration of moisture along the seam.
An alternate method of joining adjacent sheets of membrane roofing material employs tape composed of a single layer of an uncured elastomeric material which cures in place after application. This tape is applied along the edge of one of the sheets to be joined and the two sheets are then overlapped. A roller is rolled along the joint to press the sheets into engagement with the tape. The tape, however, has a limited shelf life and may even cure before it can be used if left for prolonged periods on a hot roof or in an excessively warm storeroom.
Once the sheets of membrane roofing material have been joined to cover the roof, the membrane must be fixe d in position. The spliced membrane may be held in position by means of fastening bars which are elongated strips of materials such as plastic or metal. The fastening bars are positioned in the desired location, which may overlay a lap joint, and fastened to the undelying roof structure by fasteners such as screws which extend through the membrane roofing material. In order to prevent moisture seepage, a layer of caulking material is applied to the bottom of the fastening bar prior to fastening it in place, and the heads of the fasteners are caulked after they have been inserted through the fastening bar. Some roofing manufacturers have also attempted to prevent leakage by covering the fastening bar with a strip of membrane roofing material applied with the contact cement and sealed with the roofing caulk as described above with respect to the splicing of the membrane.
Emergency repairs of membrane roofing are frequently accomplished by application of a solution of an asphalt-type material. A permanent repair may later be accomplished by removing the patched section of the membrane roofing material and splicing a new piece of material in its place.